-
A third of the land on our planet is
desert. These great scars on the face of our
planet appear to
be
lifeless.
But
surprisingly,
none
are.
In
all
of
them
life
manages,
somehow,
to
keep
a
precarious(a
dj.
危险的；不确定的
) hold.
DESERTS
Narrator
David Attenborough
Not all deserts are hot.
Fifty-mile-an-hour blowing in from Siberia brings
snow to the Gobi
desert in Mongolia.
From a summer high of 50 degrees centigrade, the
temperature in
mid-winter can drop to
minus 40, making this one of the harshest(adj.
严厉的；严酷的；刺耳
的；
粗糙的；
刺目的
) deserts of all. Few animals
can survive this extreme change. Wild Bactrian
camels(
双峰驼
), one
of the rarest animals on the planet, and perhaps
the hardiest(
adj.
能吃
苦耐劳的，
坚强的
(
hardy
的最高级
)
；
（植物等）
耐寒的
). Their
biggest problem is
lack of water,
particularly in winter when the little drop of
water is locked up as ice. Surprisingly,
snow here never melts. The air is just
too cold and too dry for it to do so. The
sun
’
s rays turn it
straightly into vapor. It
evaporates(
升华
). But it is
the only source of water so Bactrian camels
eat it. Elsewhere in the world, a camel
at a waterhole can drink as 200 litres of water
during a
single visit. Here, the
strategy is to take little and often and for good
reason, for filling the
stomach with
snow will be fatal. The camels must limit them to
the equivalent of just 10 litres of
water a day. Winter is the time for
breeding. This extraordinary performance is a male
Bactrian
camel
’
s
way of attracting the attention of passing female.
In summer, the camel cannot
stray(
vi.
走失；
偏离正题；
走入歧途；
（
已婚者或有固定关系者）
有外遇
) far from
the water hole. But now, with mouthfuls
of snow lying everywhere, they can reavel widely
in
search of mates. Today, less than
1000 of these desert specialists remain in the
wild. The
Gobi, hostile though it is,
is their last stronghold.
There
’
s no other desert
quite like the Gobi.
But why is this
place desert? There
’
s one
simple and massive cause. The Himalayas. Clouds
blowing from the south hit this
gigantic barrier. As they
’
re
forced upwards, so they empty their
moisture on the slope, leaving little
for the land on the other side. From space,
deserts are very
conspicuous(
adj.
明显的；
显而易见的；
惹人注意的；
显目
). Dunes(
[
电影
]
沙丘；
沙
丘魔堡
) of sands
hundreds of miles long streak their surface. With
no cloak(
n.
披风，斗
篷；
外套；
借口，
掩饰；
覆盖物
) of vegetation to concea
l(
vt.
隐藏，
隐瞒，
遮住
) them,
strange
formations are exposed in the naked rock.
Africa
’
s Sahara is the
largest desert of all.
It’s
the size of the United States, and the biggest
source of sands and dust in the entire world.
Sandstorms like these appear without
warning and reduce visibility for days in areas
the size
of Britain.
Dromedaries(
单峰驼
), single-hum
ped(
n.
（驼）峰，（人的）驼背；
动物背
部的隆肉；
小土丘，
圆岗；
[
< br>铁路
]
驼峰调车场
)
camels take this storm in their
stride(
n.
大步，阔步；
步幅；
进展；
一跨（的宽度）
). The heavy sand
rises only a few meters
above the
ground. But the dust can be blown 5000 meters up
into the sky. The ferocious(
adj.
残忍的；
极度的；
凶猛；
恶
)
sand, armed with grains of sands is the agent that
shapes
all deserts. Reptiles have
armored(adj.
装甲的
), scaly(a
dj.
（动物）多鳞的；
（皮肤）干
燥粗糙的；
鳞片状
) skins that protect them
from the stinging(
adj.
刺一样的，刺
人的，
激烈的
) grains. For insects,
the bombardment(
n.
炮击，轰炸
) can be very severe indeed.
The
only escape is below the surface. As the winds
rise and fall,
swirl(vt.
使成漩涡；
使眼
花；
打转；
弯曲盘旋
) and
eddy(
vt.&
vi.
起漩涡，
旋转
), so
they pile the sand into dunes.
These
sand seas can be hundreds of miles across. In
Namibia, the winds have built some of
the biggest dunes in the world. Star
dunes like these can be 300 meters high. Grains
swept up
the
flanks(
n.
侧面；
侧腹；
侧边；
侧翼
) are blown off the
crests(
n.
山顶；
羽毛饰；
鸡
冠；
（动物的）颈脊
) of the ridges(
n.
背脊，峰，隆起线；
山脊，山脉，海脊；
高
压脊；
皱摺，
田埂
), so
it
’
s only the top that is
moving. The main body of these dunes may not
have shifted for 5000 years. Few rocks
can resist the continuous blast of the sand-
carrying
wind. These outcrops are
outstanding in Egypt’s White Desert.
But they will not do so for much
long.
They’re inexorably
(
adj.
无情的；
不
可阻挡的；
坚决不变的
) chiselled(
adj.
凿过的
(
形如凿刀
的；轮廓清楚的
)
) away and turned
into more sands. Now lumps(
n.
块；团；
笨重的人；
瘤
v.
使成块；
形成团状；
归并；
(
笨重地
)
移动
< br>) of heavily eroded rocks have
been
marooned(
n.
褐红色；鞭炮；被放逐到孤岛的人
) in a sea of sand. These jagged
pyramids, 100 meters tall, were once a
part of continuous rocky plateau. The blasting(
n.
爆破；
鼓风；
喷
砂法；
) sand will eventually eliminate
them altogether. The relentless power of wind
ensures that the face of a desert is
continually changing.
But there’s one
constant present. The
desert sun.
The sun’s heat and power to evaporate
water has
had a profound effect on
bodies
and habits on everything living
here. This sun, potentially, is a killer. And the
red kangaroo
must acknowledge that.
Right now, while the sun is low,
there’s no immediate cause for
concern.
But this situation won’t last
long.
Australia is the most
arid(
adj.
干燥的；不毛
的；
枯燥的；
) continent with blistering(
adj.
快的；酷热的；起泡的；激烈的
)
daytime temperature. Every hour, the
temperature rises by 5 degrees
centigrade. Soon the heat will reach a
critical point. Any kangaroo put in the
open is in serious danger of
overheating. In the full sun, the temperature on
the
ground soars to 70 degrees. By
midday, the radiation is so intense that they
must take shelter. In the shade,
they’re shielded from much of the sun’s energy,
but their temperature can still rise.
So they lick(
v.
舔；轻拍；击败；掠过
) saliva
onto their forearms
where there’s a network of blood vessels close to
the
surface of skin, and as the
saliva(
n.
唾液
)
evaporates, the blood is cooled. This
thermal image shows how effectively the
process is. The blue area on the boby
are cooler parts. As the saliva, it
must be replaced. And this a real drain on the
kangaroos
’
body
fluids. Even in the shade, the earth is baking
hot. So the
kangaroo dig away the hot
topsoil(
n.
表层土
) to
get at the cooler ground
beneath. By
staying in the shade and licking to control their
body temperature,
kangaroos manage to
get through the hottest part of the day without
heatstroke. But for majority of the
desert animals, this strategy would not be
enough for survival. The extraordinary
ears of the fennec foxes(
n.
[
动
]
一种非洲
产的大耳小狐
) of Africa radiate heat, but the
animal have another way of
keeping
cool. They spend their days on the ground and only
emerge at sunset.
Darkness brings huge
changes. In Sahara, the temperature can drop as 30
degrees centigrade.
So it’s
cool enough
to allow
these desert fox cubs to
play. All sorts of creatures now
appear, including some really unexpected ones.
Toads(
n.
蟾蜍；癞蛤蟆
) have permeable(
adj.
可渗
透的；可穿透的
) skins and
would
quickly die from
desiccation(
n.
干燥
)
in the daytime heat. It’s only now
that they can leave shelter. The same
is true for scorpions(
n.
蝎子；心
黑的人；
蝎子鞭
), even though their
shells are actually watertight. In fact, most
small
desert creatures are nocturnal(
adj.
在夜间的；（指生物）夜间活动的
).
So it’s
only now that you
can judge that how much life there can be in a
desert. But
moisture lost, even at
night, has to be replaced sometime, somehow. And
that
problem dominates all desert dwell
ers(
n.
居民；居住者
).
The
Atacama(
阿塔卡
玛沙漠
)
desert in
Chile(
n.
智利
). This
is the driest desert in the world. Some
parts may not see rain for 50 years,
and with such a record, you would expect
a place to be completely barren. These
are South America’s camel,
guanacos(
n.
产于南美
Andes
山脉的骆马之类，原驼
). They are very
good at
conserving moisture, but they,
nonetheless(
adv.
尽管如此
< br>(
仍然
)
), need a
regular supply of water. They get it
partly from
cactus(
n.
仙人掌
)
flowers. But
that explanation raises
another question. How do the cacti(
n.
仙人掌名词
cactus
的复数形式
.
) survive without rain? Hot
winds suck all the moisture from
the
surface of the land. Clearly, they must be
something else that takes the
place of
rain. The secret is the cold sea current that runs
parallel to the land.
The cold water
cools the moisture, warm air above it and that
produces
banks(
；
一团
) of
fog. At the same time, wind blowing onto the shore
sweeps the fog
inland. Before long, the
cacti are dripping with water
dew(
n.
露水
). The
fog is so
regular that the moisture-
loving
lichens(
n.
地衣；青苔
)
are able to grow on the
cacti and they
absorb liquid like a sponge. In the land of almost
no rain, these
precious droppings are
lifesavers for many different creatures. Further
inland,
the air remains so warm that
its moisture does not condense(
v.
浓缩；
凝结；
缩短
).
So this
slender(
细长的；苗条的；
) strip of
desert is virtually the only part of
Atacama when life can exist. And
without fog, this land, too, would be empty.
The guanacos make most of the dew. But
it will not remain for long. In an hour
or two, the sun will have burnt it off
and dried the surface of cacti. The Sonoran
Desert(
n.
索诺兰沙漠（位于加利福尼亚州）
) in Arizona
is not quite so dry as